1. Field of the Invention
The present invention relates, generally, to communication systems and processes which use radio frequency (RF) transmitters and receivers (transceivers), and, in particular embodiments, to multi-service systems and processes with communication and Global Positioning System (GPS) capabilities that share functional blocks to minimize size, weight, complexity, power consumption, and cost.
2. Description of Related Art
It has become increasingly important to minimize the size, weight, complexity, power consumption, and cost of various electronic devices, especially personal communication devices such as cellular telephones, personal pagers, cordless telephones, and the like. One way to minimize such characteristics is to minimize the number of components and functions required in the electronic device, or to perform multiple functions using the same components. However, personal communication devices such as cellular telephones often require complex circuitry with a number of power-inefficient components for performing particular functions. This is especially true in modem cellular communications, where several different communication standards are employed worldwide, and cellular telephones with the flexibility to operate under multiple communications standards are highly desirable from a consumer and manufacturing perspective.
For example, GSM900 (Global System for Mobile 900) is a digital cellular standard operating in the 900 MHz frequency band that is currently used in Europe and Asia. DCS1800 is another digital cellular standard based on GSM technology, operating in the 1800 MHz frequency band and also currently used in Europe and Asia. The United States uses PCS 1900, a third digital cellular standard similar to DCS 1800, but operating in the 1900 MHz band. Multi-band cellular telephones capable of operating under all of these standards afford consumers widespread applicability and allow manufacturers to benefit from the cost-efficiency of a common design.
However, multi-band cellular telephones present a number of design challenges. Conventional single-band transmitters typically require two separate frequencies, a fixed intermediate frequency (IF) for modulation and a tunable RF for upconversion. Conventional single-band receivers also typically require two separate frequencies, a tunable RF for downconversion and a fixed IF for demodulation. Thus, a single-band cellular telephone may require as many as four different frequency sources. Multi-band cellular telephones exacerbate the problem because the modulation, upconversion, downconversion, and demodulation processes for each band may require different frequencies. Furthermore, the different frequencies employed by each band may require different filters for the transmit and receive function of each band.
The portability of cellular telephones has led to additional design challenges unrelated to the basic function of the cellular telephone. In the nationwide 911 system for reporting emergencies, 911 operators are typically provided with the location of the telephone from which the 911 call was initiated to assist emergency personnel in responding to the distress call. However, because cellular telephones are mobile, current methods for tracing 911 telephone calls are unable to provide location information when the call is made from a cellular telephone. This problem is not insignificant, for studies have shown that 30-40% of all 911 calls are made from cellular telephones. To address this problem, the Federal Communications Commission (FCC) has mandated that, by the end of the year 2001, cellular service providers must provide the ability to automatically locate cellular telephones calling 911 to within about 20 meters in addition to basic cellular communications. This location identification capability is referred to in the industry and herein as E911 support.
Even in non-emergency situations, knowledge of the location of a cellular telephone is of keen consumer interest. Travelers in unfamiliar areas may use their cellular telephone to both identify their present position and receive instructions on how to proceed to their desired destination. Conversely, those in unfamiliar territory may use their cellular telephone to identify their present position and assist others in locating them. A cellular telephone capable of providing positioning information may benefit the business traveler who encounters a rental automobile equipped with a navigation system able to utilize such positioning information. Real estate agents, delivery services, and the like may be able to use positioning information to locate houses or businesses.
Thus, both the FCC--imposed requirement and consumer--driven need for cellular telephone positioning information have created a market for cellular telephones with multi-service capabilities, increasing the design challenge of producing cellular telephones of minimal size, weight, complexity, power consumption, and cost.